Receivers are used in many applications to receive incoming radio frequency (RF) signals and convert them to baseband signals for desired processing. Various such receivers exist including cellular receivers, radio receivers, satellite receivers such as television satellite receivers, among many others.
A receiver is typically coupled to receive incoming RF signals from an antenna and process the signals in various stages, including amplification stages, filtering stages, downconversion stages and the like. In a satellite system, such as a direct video broadcasting (DVB) system, an RF spectrum of a very wide band, e.g., approximately 1.3 gigahertz (GHz), includes many individual channels carrying programming. Typically, these channels are separated by some predetermined spacing, and the bandwidth of given channels can vary. A receiver will include a list of available channels within the RF spectrum, their center or carrier frequencies, and corresponding symbol rates, among other such information.
While in many countries this information remains fixed, in other countries, center frequencies and baud rates can change over time. Accordingly, a receiver can include functionality to search for and locate available channels. Such operation is typically referred to as a blind scan. A blind scan is used to establish a list of valid channels with sufficiently estimated carrier frequencies and baud rates for a given frequency band and symbol rate range. However, existing blind scan functionality is relatively inefficient and requires significant time to perform analysis of an RF spectrum, such as a satellite spectrum. This excessive time is incurred as typical blind scans exhaustively scan all possible combinations of frequency shifts and symbol rates to find every possible channel within a given frequency band and baud rate range. Such blind scans generally use a non-linear transform analysis, meaning that the original data has undergone some sort of non-linear transform, the results of which are then analyzed in the frequency domain. However, because of the presence of adjacent channels, inter-modulation products confuse the analysis, as do the effects of filtering and aliasing.
Still further, in known satellite systems when acquiring a desired channel, a dish antenna, e.g., a low noise block (LNB) antenna, is often off by a large frequency from the proper frequency for a selected channel. Such frequency errors can lead to poor performance, or even the inability to properly tune a desired channel.
Thus a need exists for improved blind scan processing, as well as a manner to improve frequency acquisition of a desired channel.